The present invention relates to a position detecting method, and more particularly, though not exclusively, to a method for detecting a position of an alignment mark provided on a wafer. The present invention is suitable, for example, for manufactures of various devices including semiconductor chips such as ICs and LSIs, display devices such as liquid crystal panels, sensing devices such as magnetic heads, and image-pickup devices such as CCDs.
Recent high-performance and inexpensive electronic apparatuses need more economic and precisely manufactured semiconductors installed in them, and require an exposure apparatus that exposes a semiconductor circuit pattern to have precision and efficiency in the transfer of a circuit pattern of a reticle or a mask (collectively referred to as a “reticle” hereinafter) onto a wafer and a glass plate (collective referred to as a “wafer” hereinafter), onto which a photosensitive material (referred to as “resist” hereinafter) is applied. In general, precise exposure of a circuit pattern requires a precise alignment between the reticle and the wafer.
A conventional alignment method exposes alignment marks on a wafer at the same time when the circuit pattern of the reticle is exposed, and sequentially measures positions of plural preset alignment marks among the alignment marks formed on the wafer after the exposure process, using an alignment detection optical system. After the position measurement result is statistically processed to calculate the entire shot arrangement, and the wafer is positioned in relation to the reticle based on the calculation result.
The alignment marks are indexes to align the reticle and the wafer with high precision. Recent fine processing to circuit patterns requires a precise alignment mark. The special semiconductor manufacturing technology, such as a chemical mechanical polishing (“CMP”) process, has been recently introduced. Along with this, a wafer induced shift (“WIS”) as a positional detection error caused by a wafer process occurs, scatters shapes of the alignment marks among wafers and among shots, and deteriorates the alignment accuracy. One solution for this problem is an offset correction to correct the WIS, as disclosed in Japanese Patent Application, Publication No. 2004-117030. The offset correction previously calculates a true position of an alignment mark and a shift amount from the alignment mark detected by a detection system, and uses the offset value to correct the position of the alignment mark detected by the detection system. The position of the alignment mark actually detected by the detection system is also referred to as an “actual position” hereinafter. Conventionally, as in Japanese Patent Application No. 2004-117030, a linear function is used to calculate the shift amount.
Other prior art relating to the position detecting method include, for example, Japanese Patent Applications Nos. 6-151274 and 8-94315.
However, the WIS occurs due to a single cause, an interaction among plural causes, and an apparatus cause, such as an exposure apparatus and an alignment optical system. Therefore, the linear function has a difficulty to predict a shift amount, or to detect a position of an alignment mark precisely. The apparatus cause is also referred to as a tool induced shift (“TIS”). An interaction between the process error and the apparatus error is referred to as a TIS-WIS interaction.